1. Field of the Invention
The invention relates to pipeline inspection and more specifically to a vehicle which can be towed through a pipeline to allow analysis of its wall structure.
2. Discussion of the Background
Large diameter pipes can be tested using complex pipeline pigs which may even operate when the pipes are xe2x80x98livexe2x80x99, i.e. when gas, for example, is flowing through the pipe.
In U.S. Pat. No. 4,292,589A an eddy current method and apparatus for lowering into an oil well casing is disclosed using transmitting coils and receiving pads.
In U.S. Pat. No. 4,203,069A an eddy current producing coil is shown for use with a rotor for concentrating the field.
In U.S. Pat. No. 5532591A an arrangement uses a rotating magnetic field to test flaws in the wall of a drinks can.
In EP0065325A a flaw detector uses eddy currents from a source coil with an associated detector.
In JP08005611A a flaw detector uses transmission and receiving coils utilising eddy current detection with reduced noise.
In JP03120457A an eddy current flaw detector uses coils for reducing the influence of an external baffle plate.
In JP61133856 a detector system uses both eddy currents and ultrasonic thickness measurement to aid diagnosis.
The present invention seeks to provide an improved arrangement which also allows both ferrous and non-ferrous small diameter pipes to be tested for defects.
According to the invention there is provided a pipeline inspection device for travelling through a pipeline and including generator means for generating an eddy current field within the pipeline; and detector means for detecting the resultant field and characterised in that the inspection device is configured to determine the presence of faults in both ferrous and non-ferrous pipelines, the detector means comprising first and second receivers spaced longitudinally on either side of a transmitter coil at a single location forming the generator means, said receivers being configured to receive information derived from the transmitter coil at two longitudinally spaced locations on the pipeline, said information being updated as the device travels through the pipeline and means being provided for selecting a coil excitation frequency dependent on the ferrous or non-ferrous nature of the pipeline to be tested.
Further according to the invention there is provided a method of testing a pipeline using a pipeline inspection device, said method including generating an eddy current in a coil in said device and detecting the eddy current induced in the wall of the pipeline and characterised by the steps of: selecting a coil excitation frequency dependent on the nature of the pipeline to allow both ferrous and non-ferrous pipelines to be tested, detecting the induced eddy current at two longitudinally spaced locations from the coil positioned at a single location therebetween and updating the information as the device travels along the pipeline to allow faults in the pipeline to be determined.